This core will serve five functions. 1) Micro-characterization, i.e., large-scale identification of post-translational modifications (Projects 1,2,3, and 5). 2) Differential display or the identification and relative quanitation of up- and down-regulated proteins between two different samples (health versus diseased) (Project 2, 3, and 5). 3) Protein-protein interactions, which will isolate and identify proteins associated in complexes (Projects 1, 2, 3 and 5). 4) Structural analysis, which will use the distance constraints for determination of a protein's three-dimensional structure (Project 1 and 5). This involves cross-linking proteins at specific functional groups, proteolytic digestion, and MS analysis. MS analysis of cross-linked peptides provides information on proximity of these peptides in three-dimensional structure. 5) The final function of the laboratory will be identification of novel products generated by mutant P450 enzymes (Project 4).